Chemoluminescence and Bioluminescence

Principle

Chemoluminescence

Chemoluminescence is the emission of light as the result of a chemical reaction. The reaction may occur in the liquid phase or in the gas phase. Most simply, given reactants A and B, with an excited intermediate ◊, the reaction is:

[A] + [B] → [◊] → [Products] + light.

The decay of the excited state[◊] to a lower energy level is responsible for the emission of light. In theory, one photon of light should be given off for each molecule of reactant, so Avogadro's number of photons per mole. In actual practice, non-enzymatic reactions seldom exceed 1% quantum efficiency. For example, in the liquid phase, if [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst the reaction is:

luminol + H₂O₂ → 3-aminophthalate[◊] → 3- aminophthalate + light.

A standard example of chemoluminescence in the laboratory setting is found in the luminol test, where evidence of blood is taken when the sample glows upon contact with iron. A daily live example is a lightstick.

Fig. 1 Lightsticks

Enzymatic chemoluminescence (ECL) is a common technique for a variety of detection assays in biology. An horseradish peroxidase molecule (HRP) is tethered to the molecule of interest (usually by immunoglobulin staining). This then locally catalyzes the conversion of the ECL reagent into a sensitized reagent, which on further oxidation by hydrogen peroxide, produces an excited triplet (a set of three quantum states of a system, each with total spin S = 1) carbonyl which emits light when it decays to the singlet (S = 0) in a carbonyl group. The result is amplification of antibody detectability.

When chemoluminescence takes place in living organisms, the phenomenon is called bioluminescence.

Applications

Analysis of organic species: useful with enzymes, where the substrate isn't directly involved in chemoluminescence reaction, but the product is a reactant of the chemoluminescence reaction. Further environmental gas and liquid analysis for determining small amounts of impurities or poisons in air. Typical example is NO determination with detection limits down to 1 ppb.

Bioluminescence

Bioluminescence is the production and emission of light by a living organism as the result of a chemoluminescence reaction during which chemical energy is converted to light energy. Bioluminescence is really a form of "cold light" emission; less than 20% of the light is generated by thermal radiation. It should not be confused with fluorescence, phosphorescence or refraction of light.

The most striking example is bioluminescence by dinoflagellates at the surface of seawater when the surface is agitation, e.g. by a swimmer or a copepode. The λ_max is at ca. 472 nm and the emittance has the remarkable efficiency of more than 50%,

Fig. 2 Image of hundreds of agar plates cultured with a species of bioluminescent marine bacteria

Bioluminescence may be generated by symbiosis organisms carried within a larger organism. It is generated by an enzyme-catalyzed chemoluminescence reaction, wherein a luceferin (a kind of pigment) is oxidized by a luceferase (a kind of enzyme). ATP is involved in most instances. The chemical reaction can be either external to cells, or an intracellular process. The expression of genes related to bioluminescence in bacteria is controlled by the lux operon.

Application

Luciferase systems are widely used in the field of genetic engineering as reporter genes (green fluorescent protein, see Fluorescence).

The structure of photophores, the light producing organs in bioluminescent organisms, are being investigated by industry (glowing trees, organisms needing watering), food quality control, detecting bacterial species and studies into potential applications as for tagging domestic animals.

More Info

All cells produce some form of bioluminescence within the electromagnetic spectrum, but most is neither visible nor noticeable to the naked eye. Every organism's bioluminescence is unique in wavelength, duration, timing and regularity of flashes.

90% Of deep-sea marine life is estimated to produce bioluminescence in one form or another. Many marine invertebrates have bioluminescence, like planktons, microbes, corals, clams, jelly fish, nudibranchs, crustaceans (lobsters, squids etc.), echinoderms (sea stars, sea urchins etc.). Most marine light-emission belongs in the blue and green light spectrum, the wavelengths that have the most powerful penetrating power in water. However, certain jawless fish emit red and IR light.

Non-marine bioluminescence is less widely distributed, but with more color variety. Well-known forms of land-bioluminescence are fireflies and New Zealand glow worms. Other insects (and larvae), worms (segmented), arachnoids, fish and even species of fungi have bioluminescent abilities.

Most forms are brighter (or only exist) at night, following a circadian rhythm.

It is thought to play a direct role in camouflage, attraction, repulsion and communication. It promotes the symbiotic induction of bacteria into host species, and may play a role in colony aggregation.

Source: Wikipedia